CABG surgery has become one of the most frequently performed operations in the United States, involving increasingly older individuals. Because neurological and behavioral disturbances after such surgery involving cardiopulmonary bypass have been observed at rates from 10 to 60 percent in centers around the world, the need exists of greater understanding of patient characteristics and intraoperative approaches that will minimize risk to the patient and mizimize surgical outcomes. This investigation will describe the neurobehavioral status of patients prior to surgery for CABG (or repair of valvular disease) and will ascertain whether control of selected intraoperative events can influence neurobehavioral outcome in a beneficial way. Neuropsychological tests sensitive to the integrity of the cerebral hemispheres will be administered to 100 subjects prior to and following surgery; 50 non-operative control subjects will be examined similarly. The neurobehavioral status of subjects will be related to recorded electrical events during surgery, variations in pH during anesthesia, and description of medical outcomes. The goals are to define the incidence and severity of organic brain dysfunction present prior to CABG surgery, determine whether the presence of preoperative impairment may influence surgical outcome, and determine whether maintaining pH near the normothermic normal value of 7.40 or at a more alkaline state during CABG under moderate hypothermic conditions facilitates a more optimal outcome.